Exosomes are small vesicles 40-100 nm in diameter, that are secreted by a number of different cell types for communicating with other cells via the proteins and ribonucleic acids they carry. An exosome is created intracellularly when a segment of the cell membrane spontaneously invaginates and is endocytosed. The internalized segment is broken into smaller vesicles that are subsequently expelled from the cell. The latter stage occurs when the late endosome, containing many small vesicles, fuses with the cell membrane, triggering the release of the vesicles from the cell. The vesicles (once released are called exosomes) consist of a lipid raft embedded with ligands common to the original cell membrane.
Depending on their cellular origin, exosomes carry uniquely distinct profiles of proteins and/or nucleic acids (such as microRNAs (miRNAs)), which can trigger signaling pathways in other cells and/or transfer exosomal products into other cells by exosomal fusion with cellular plasma membranes. The protein composition of exosomes is distinct from that of other organelles, including early endosomes and plasma membranes, more closely resembling that of late endosomes or multivesicular bodies, (MVBs).
Exosome are released from different cell types in varied physiological contexts. For example, B lymphocytes release exosomes carrying class II major histocompatibility complex molecules, which play a role in antigenic presentation. Similarly, dendritic cells produce exosomes (i.e., dexosomes, Dex), which play a role in immune response mediation, particularly in cytotoxic T lymphocyte stimulation. Some tumor cells secrete specific exosomes (i.e., texosomes, Tex) carrying tumor antigens in a regulated manner, which can present these antigens to antigen presenting cells. Exosomes may also carry pathogen-associated products. For example, exosomes have been known to carry products derived from Mycobacterium tuberculosis and Toxoplasma gondii-infected cells.
HIV and hepatitis virus infections are often assayed using serum or plasma. The detection of a specific viral antibody is presumptive evidence of a corresponding viral infection, and is typically confirmed by the Western blot procedure. For example, detection of HIV virus by p24 antigen determination or detection of viral RNA by RT-PCR is also used to determine the amount of virus in circulation. CD4/CD8 T cell ratios and other immune function tests are often used to monitor immune status and progression to AIDS. More recently, HIV tests using saliva or epithelia cells in the mouth have also been developed. However, currently there are few tests available to measure viral antigens or antibodies in urine. The detection of HIV and hepatitis proteins in the urine may provide a more rapid method to detect HIV or hepatitis virus infections and/or monitor the progression of disease, particularly viral-associated renal complications.
Hepatitis is an inflammation of the liver, most commonly caused by a viral infection. There are five main hepatitis viruses, referred to as types A, B, C, D and E. Hepatitis A and E are typically caused by ingestion of contaminated food or water. Hepatitis B, C and D usually occur as a result of parenteral contact with infected body fluids (e.g., from blood transfusions or invasive medical procedures using contaminated equipment). Hepatitis B is also transmitted by sexual contact.
Hepatitis A virus (HAV) is an enterically transmitted viral disease that causes fever, malaise, anorexia, nausea, abdominal discomfort and jaundice. HAV is normally acquired by fecal-oral route, by either person-to-person contact, ingestion of contaminated food or water or transmission by pooled plasma products. The absence of a lipid envelope makes HAV very resistant to physicochemical inactivation, and the virus can withstand conventional heat treatment of blood products. The development of sensitive and specific diagnostic assays to identify HAV antigens and/or antibodies in infected individuals as well as nucleic acid-based tests to detect viremic samples to exclude them from transfusion represents an important public health challenge.
Hepatitis B virus (HBV) infects humans and may result in two clinical outcomes. In the majority of clinical infections in adults (90-95%), the virus is cleared after several weeks or months, and the patient develops a lifelong immunity against re-infection. In the remaining cases, however, the virus is not eliminated from the tissues, and the patient remains chronically infected. The sequelae of chronic infection are serious: such individuals are highly likely to develop scarring of the liver tissue (cirrhosis) and may eventually develop hepatocellular carcinoma. HBV is transmitted via infected blood or other body fluids, especially saliva and semen, during delivery, sexual activity, or sharing of needles contaminated by infected blood.
Worldwide, it is estimated that 400 million people are chronically infected with hepatitis B virus (HBV). Chronic hepatitis B (CHB) infection is the most common cause of liver cirrhosis and hepatocellular carcinoma (HCC), with an estimated 500,000-900,000 deaths per year. Continuing HBV replication increases the risk of progression to cirrhosis and HCC.
Hepatitis C virus (HCV) is the causal agent for a largely chronic liver infection originally identified as non-A, non-B hepatitis. HCV has infected about four million people in the United States and 170 million worldwide, about four times as many as HIV and accounts for 90 to 95% of the hepatitis attributable to blood transfusion. It is presumed that the primary route of infection is through contact with contaminated bodily fluids, especially blood, from infected individuals. HCV infection is one of the primary causes of liver transplantation in the United States and other countries. Approximately 40-50% of the liver transplants in the United States are based on HCV infections. The disease frequently progresses to chronic liver damage. While the pathology of HCV infection affects mainly the liver, the virus is found in other cell types in the body including peripheral blood lymphocytes.
The hepatitis delta virus (HDV) is a satellite RNA virus dependent on hepatitis B surface antigens to assemble its envelope and form new virions to propagate infection. HDV has a small 1.7 Kb genome making it the smallest known human virus. However, HDV is the most severe form of viral hepatitis. Compared with other agents of viral hepatitis, acute HDV infection is more often associated with fulminant hepatitis, a rapidly progressive, often fatal form of the disease in which massive amounts of the liver are destroyed. Chronic type D hepatitis is typically characterized by necroinflammatory lesions, similar to chronic HBV infection, but is more severe, and frequently progresses rapidly to cirrhosis and liver failure, accounting for the disproportionate association of chronic HDV infection with terminal liver disease. Although HDV infection affects fewer individuals than HBV alone, the resulting acute or chronic liver failure is a common indication for liver transplantation in Europe as well as North America. Chronic HDV disease affects 15 million persons worldwide, about 70,000 of whom are in the U.S. The Centers for Disease Control estimates 1,000 deaths annually in the U.S. due to HDV infection.
In view of the wide scope of individuals affected by infectious agents, including various HIV and hepatitis-virus isolates, and the lack of reliable, rapid, cost-effective and less invasive diagnostic tests, there is a need for diagnostic tests for diagnosing infectious agents and infectious disease conditions that is reliable, rapid, cost-effective and less invasive.